1. Field of the Invention
The present invention relates to a recording apparatus which scans a recording head to record an image on a recording medium.
2. Related Background Art
A printer which records characters and images on a sheet material (recording medium) such as a record sheet or plastic sheet has been known, and an image forming process adopted in such a printer includes a wire dot system, an ink jet system and a laser beam system. Such a printer includes a serial type in which a carriage carrying a recording head is scanned to record, a line print type in which a line head is used to print by line and a page print type in which recording is made by page. Of those, in a serial ink jet printer, an ink jet head (recording head) is mounted on a carriage which is laterally and reciprocally driven by a carriage motor along a longitudinal direction of a platen, and the ink jet head is driven in synchronism with the scan of the carriage so that ink is discharged from ink discharge nozzles to form an image on a record sheet.
As a demand for high quality recording recently increases, the recording head becomes more and more high density and an ink jet printer equipped with an ink jet head (recording head) having nozzles (recording elements) of 360 dots per inch (dpi) has become common, and plain papers as well as the sheet material specially designed for the ink jet are permitted for printing. As the recording density of the recording head increases, a process of receiving image data in bit form and recording it in graphic has become common.
In order to record such graphic data with a high quality by a serial printer, white stripes or black stripes which appear along the reciprocal movement direction of the carriage (main scan direction) and along a sub-scan direction orthogonal to the main scan direction should be prevented. Where the printer is a color printer, the generation of color irregularity in the recorded image should also be prevented.
When printing is made on a recording medium such as a plain paper or an OHP sheet, the absorption of ink is worse than the sheet specially designed for the ink jet so that a time for the ink to be fixed on the recording medium should be reserved. To this end, a density of ink deposited on the recording medium in a predetermined time must be reduced. However, in the color printer, since inks of different colors are recorded at the same position, it is difficult to lower the ink density below a certain level.
In order to solve the above problem, as shown in FIG. 16, nozzles of a recording head having 64 nozzles are divided into L blocks (L=4, L.gtoreq.22 in FIG. 16) and a recording medium is transported along the sub-scan direction for each block of the divided nozzles. The recording head is reciprocally scanned along the main scan direction L times to record an image of a width (band) which can be recorded by one scan of the recording head to accomplish so-called multi-pass recording. In FIG. 16, numeral 800 denotes recording in a first pass, and the recording head is positioned at that position. Numeral 801 denotes a second pass at which the recording medium is transported by 16-nozzle length along the sub-scan direction. Similarly, numeral 802 denotes a third pass, numeral 803 denotes a fourth pass and numeral 804 denotes a fifth pass.
Since recording is to be made at different positions on the recording medium by using different nozzles in the respective passes, a continuous repetitive pattern of M.times.N dots (16.times.16 in FIGS. 17 to 20) is prepared for each record pass as shown in FIGS. 17 to 20 and recording is made while the record data is masked for each record pass. FIG. 17 shows a first pass pattern, FIG. 18 shows a second pass pattern, FIG. 19 shows a third pass pattern and FIG. 20 shows a fourth pass pattern. In FIGS. 17 to 20, when recording data are on black dot positions, ink is discharged from the corresponding nozzles, and at white dot positions, the discharge of the ink is masked even if the record data is on those positions and the ink is not discharged. Optimum size of the repetitive pattern (the values of M and N) and the mask pattern thereof may differ from printer to printer or from record mode to record mode. In the past, such mask operation has been conducted by software. In addition, the data transfer from a memory which stores the record data to the recording head has also been conducted by software.
In the prior art apparatus, since the mask operation to control the discharge of ink from the nozzles of the recording head and the data transfer operation were conducted by software, the following disadvantages were included:
(1) Since the operation of the mask data is required when the record data is to be outputted, the load to the software increases and high speed recording cannot be attained.
(2) The record data of one-pass must be prepared by the mask operation before the carriage is scanned for recording. As a result, a memory area to store an additional line of record data is required and a cost is increased.
(3) Since the mask operation and the data transfer operation are conducted by software, the software processing time increases and an effective recording speed (throughput) is lowered.